FIGS. P1a and P1b illustrate a schematic view of a typical Heat-Rejection Device (HRD) (e.g., a residential/commercial air conditioner outdoor unit). Such a unit typically consists of a refrigerant compressor, a surrounding condenser coil, and an internal condenser fan. FIG. P2 is a schematic view of the same typical HRD, with additional layers depicting its internal condenser fan, as well as the approximate airflow pattern that it produces. The fan draws in air through its 4 side condenser surfaces and discharges it vertically (along +y axis). As the air is drawn through the condenser surfaces (“coils” and “fins”), heat within the condenser is transferred to the air and is subsequently rejected to atmosphere as the hot air exits the top. Some HRDs use water cooling to increase efficiency.
The benefits of water cooling have been known and exploited for many years. The key to water's power in cooling comes from its phase change from a liquid to a vapor, wherein it absorbs a great amount of “heat of vaporization.” This type of heat is referred to as “latent” heat. Water cooling is sometimes avoided because it usually involves the addition of large industrial infrastructure, but new manufacturers and technologies are working to improve the economics for water-cooling smaller systems. In general, this evaporative cooling effect can apply to essentially any liquid (not just water), when it evaporates into another gaseous medium (including but not limited to air).
In many climatic regions, the water-cooling may reduce condenser temperatures (and thus pressures) more efficiently than air cooling. This reduces the discharge pressure (or “head”) of the compressor, and consequently the load (or “lift”) of the compressor, allowing the system to deliver the same cooling power with less input power. Such compressors are typically driven by an electric motor; the motor is typically an “induction” motor, running on alternating current (AC). The electrical power consumed by the motor increases with increasing load on the compressor it is driving. This electrical power (P) is proportional to motor's electrical supply voltage (V), its resulting electrical current draw (I), and its resulting power factor (PF):P˜V*I*PF.
When compressor load is reduced, P is reduced through reductions in both current (I) and power factor (PF): a common behavior of AC motors which arises according to the laws of electrodynamics. However, common mnemonics are often used to visualize this electrical behavior through the behavior of water: voltage (V) is analogous to the pressure driving a water stream; and current (I) is analogous to the flow rate of the water stream. Unfortunately, fewer analogies exist to help describe power factor (PF). In short, power factor relates the phase relationship between the AC voltage and current waveforms: when the two waveforms are perfectly in phase (or in “synch”), their power factor is 1; when the two waves are perfectly out of phase (completely not in synch), their power factor is 0. As an AC motor approaches full load, its power factor approaches 1 (say ˜80% to 90%); as its load decreases, so does its power factor (˜75% or less).
Conventionally, common evaporative cooling systems comprise water nozzles that spray water mist onto the surface of the HRD (assumed to be a condenser hereafter). This spraying configuration is often difficult to adjust geometrically, as the mist is most effective when applied in a homogeneous pattern that perfectly contacts all of the surfaces of the condenser. Multiple spray nozzles are often implemented to mitigate this challenge; as a result, some sections of the condenser surface may be “over sprayed,” receiving more water than necessary which hence forms droplets that deflect or fall down the surface as waste. Moreover, spray nozzles are susceptible to clogs and fouling from water deposits, which hinder their effectiveness; the clogs distort the spray pattern's geometry as well as its intended flow rate.